1. Field of the Invention
The present invention relates to airway pressure support systems, and, more particularly, to a methodology for automatically titrating the pressure for patients, particularly where sleep disordered breathing (SDB) presents complex symptoms.
2. Description of the Related Art
Many individuals suffer from disordered breathing during sleep. Sleep apnea is a common example of such sleep disordered breathing suffered by millions of people throughout the world. One type of sleep apnea is obstructive sleep apnea (OSA), which is a condition in which sleep is repeatedly interrupted by an inability to breathe due to an obstruction of the airway; typically the upper airway or pharyngeal area. Obstruction of the airway is generally believed to be due, at least in part, to a general relaxation of the muscles which stabilize the upper airway segment, thereby allowing the tissues to collapse the airway. Another type of sleep apnea syndrome is a central apnea, which is a cessation of respiration due to the absence of respiratory signals from the brain's respiratory center. An apnea condition, whether OSA, central, or mixed, which is combination of OSA and central, is defined as the complete or near cessation of breathing, for example a 90% or greater reduction in peak respiratory air-flow.
Those afflicted with sleep apnea experience sleep fragmentation and complete or nearly complete cessation of ventilation intermittently during sleep with potentially severe degrees of oxyhemoglobin desaturation. These symptoms may be translated clinically into extreme daytime sleepiness, cardiac arrhythmias, pulmonary-artery hypertension, congestive heart failure and/or cognitive dysfunction. Other consequences of sleep apnea include right ventricular dysfunction, carbon dioxide retention during wakefulness, as well as during sleep, and continuous reduced arterial oxygen tension. Sleep apnea sufferers may be at risk for excessive mortality from these factors as well as by an elevated risk for accidents while driving and/or operating potentially dangerous equipment.
Even if a patient does not suffer from a complete or nearly complete obstruction of the airway, it is also known that adverse effects, such as arousals from sleep, can occur where there is only a partial obstruction of the airway. Partial obstruction of the airway typically results in shallow breathing referred to as a hypopnea. A hypopnea is typically defined as a 50% or greater reduction in the peak respiratory air-flow. Other types of sleep disordered breathing include, without limitation, upper airway resistance syndrome (UARS) and vibration of the airway, such as vibration of the pharyngeal wall, commonly referred to as snoring. Thus, in diagnosing a patient with a breathing disorder, such as OSA, central apneas, or UARS, it is important to detect accurately the occurrence of apneas and hypopneas of the patient.
Devices are known that attempt to detect apneas and hypopneas to determine in real time whether a patient suffers from a sleep apnea syndrome. Examples of conventional apnea/hypopnea detection devices are described in U.S. Pat. No. 5,295,490 to Dodakian; U.S. Pat. No. 5,605,151 to Lynn; U.S. Pat. No. 5,797,852 to Karakasoglu et al.; U.S. Pat. No. 5,961,447 to Raviv et al.; U.S. Pat. No. 6,142,950 to Allen et al.; U.S. Pat. No. 6,165,133 to Rapoport et al.; U.S. Pat. No. 6,368,287 to Hadas.
It is further well known to treat sleep disordered breathing by applying a continuous positive air pressure (CPAP) to the patient's airway. This positive pressure effectively “splints” the airway, thereby maintaining an open passage to the lungs. It is also known to provide a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient's breathing cycle, or varies with the patient's effort, to increase the comfort to the patient. This pressure support technique is referred to as bi-level pressure support, in which the inspiratory positive airway pressure (IPAP) delivered to the patient is higher than the expiratory positive airway pressure (EPAP).
It is further known to provide a positive pressure therapy in which the pressure is automatically adjusted based on the detected conditions of the patient, such as whether the patient is experiencing an apnea and/or hypopnea. This pressure support technique is referred to as an auto-titration type of pressure support, because the pressure support device seeks to provide a pressure to the patient that is only as high as necessary to treat the disordered breathing. Thus, the effectiveness of treating a patient via an auto-titration type of pressure support system can depend to a great extent on the accurate detection of apneas and/or hypopneas.
Examples of conventional auto-titration pressure support system are disclosed in U.S. Pat. No. 5,245,995 to Sullivan et al.; U.S. Pat. Nos. 5,259,373; 5,549,106, and 5,845,636 all to Gruenke et al.; U.S. Pat. Nos. 5,458,137 and 6,058,747 both to Axe et al.; U.S. Pat. Nos. 5,704,345; 6,029,665, and 6,138,675 all to Berthon-Jones; U.S. Pat. No. 5,645,053 to Remmers et al.; and U.S. Pat. Nos. 5,335,654; 5,490,502, 5,535,739, and 5,803,066 all to Rapoport et al. All of these conventional pressure support systems, with the possible exception of U.S. Pat. No. 5,645,053 to Remmers et al., are reactive to the patient's monitored condition. That is, once a condition occurs that indicates abnormal breathing, the system alters the pressure support to treat this condition.
The spectrum of disease states that cause and affect sleep disordered breathing is as far ranging as it is complicated. Complex patients, for example, patients with Cheyne-Stokes Respiration, Opioid-Induced Central Sleep Apnea, CPAP-Emergent Sleep Apnea, etc., are currently treated with either BiPAP S/T devices (BiPAP devices with fixed backup rates) or with ASV devices, as described for example in U.S. Pat. No. 6,532,959 to Berthon-Jones, U.S. Pat. No. 6,752,151 to Hill, and U.S. patent application Ser. No. 11/235,520 (publication no. 2006-0070624-A1) to Kane. While complex patients are often treated quite adequately on BiPAP S/T devices and ASV devices, both types of devices require a physician to titrate a portion of the therapy (EPAP and IPAP in the case of BiPAP S/T devices and just EPAP in the case of ASV devices). Most typically, EPAP is titrated to reduce obstructive activity, especially obstructive apneas and severe obstructive hypopneas. IPAP and backup rate are used (mostly automatically in the ASV device) to treat the remaining mild obstructive activity and the central activity, e.g., central apneas and hypopneas.
The physician interaction is required for titration of EPAP because, even with a smarter device (such as ASV), titrating EPAP on a complex patient is a difficult task that requires making decisions concerning the type of events that are being incurred, etc. Mistakes in titrating the pressure can are made in this process, due, for example, to human error on the part of sleep technicians doing the work. While some physicians are able to perform the titration correctly, many have difficulty. Thus, there is a need for an improved methodology for titrating pressure support systems that can, for example, more effectively treat patients that are regarded as complex. More specifically, there is a need for an improved methodology for automating the difficult process of titrating EPAP (or CPAP on an AutoCPAP device) on a complex patient.
In one embodiment, a method of providing pressure support to a patient is provided that includes detecting an occurrence of a sleep disordered breathing event in the patient, and, in response to the detecting, titrating a pressure of a flow of gas provided to the patient based on at least two of: (i) a determined patency of an airway of the patient, (ii) a determined cause of the sleep disordered breathing event, and (iii) a determined responsiveness of the patient to previous pressure changes in the flow of gas provided to the patient.